1. Field of the Invention
The present invention relates to a method of and an apparatus for stretching a tubular thermoplastic polymer film biaxially or longitudinally and transversely at the same time.
2. Prior Art
A variety of methods and apparatus have been known for continuously stretching a tubular film biaxially in longitudinal and transverse directions.
Some representative prior art methods and apparatus are shown in the following patents:
British Pat. No. 1,113,136, patented May, 8, 1968; U.S. Pat. No. 3,472,924, patented Oct. 14, 1969; and U.S. Pat. No. 3,581,344, patented June 1, 1971.